Multi-pocket filter

ABSTRACT

A filter element, as in a filter bag, comprises a pocket having partitions between the side walls to form pocket portions. The margins of the partitions are welded ultrasonically to the inner surface of the layers. The inlet end of the partitions may be split into flaps to ease connection of the bag to a header frame. A simple yet effective method and apparatus may be utilizable to make the filter element, and a bag including it.

This application is a divisional application of Ser. No. 09/229,268filed Jan. 13, 1999, now U.S. Pat. No. 6,159,316.

The invention relates to the filtration of gases, typically of air toremove dust particles.

The particles may range from about 0.3 to about 30 micron in size.

It is known to make a gas filter bag from gas permeable natural materialin the form of generally parallel pockets. The pockets have an openupstream inlet and a closed bottom end, the intention being that thedust particles will be trapped in the closed end of the pockets as thegas flow passes therethrough. The pockets may be defined by longitudinalseams formed by stitching. Usually a hot melt adhesive is applied overthe stitched holes to seal them to avoid escape of particles. This is alabour intensive manufacturing method and the gas entrapment propertiesare not very good. It is one object of the invention to provide a gasfilter of improved performance.

According to the invention in one aspect there is provided a gas filterelement comprising

two side walls forms of gas permeable material joined along three oftheir sides to define a pocket having an upstream open inlet and adownstream closed end, characterised in that, generally parallelpartitions bridge the opposite side walls to define individual pocketportions extending from the inlet end to the closed end, marginalportions of the partitions being secured to the inside of the sidewalls, whereby in use the air filter elements exhibits a low pressuredrop and a high degree of dust efficiency and dust holding capacity.

The walls may be made of any suitable material which may be wholly ormainly synthetic fibres. Because the partitions are joined to the wallsby a welding process, the material should be fusible (or at leastportions thereof should be).

Preferably the partition is a thin generally planar strip of fusiblematerial which in use presents a narrow edge to the flow of air.

Preferably the marginal portions are secured to the inner surface of theside walls by ultrasonic welding.

Preferably a short length portion of one edge of the partition adjacentthe open inlet end is not joined to the inner surface of the adjacentwall to permit flexure of the front end of the pocket so that it mayeasily be mounted in say a filter header frame. Alternatively and morepreferably an elongated slit is formed in the upstream and portion ofthe partition to provide two flaps which enable the pocket to be openedin the manner of a jaw to engage the frame. The length and shape of theslit will be determined according to each filter element and frame,which typically is a header frame.

In another aspect the invention provides a continuous method of making asuccession of pockets for a gas filter element, the method comprising:

advancing two elongate webs of synthetic fibre material to a workstation to lie on opposite sides of an ultrasonic welding unit,

advancing parallel strips of fusible material to extend generallyparallel to each other and to be positioned between the webs andsubstantially at right angles to the major axis of the webs;

passing the strips through a former to fold up the longitudinal marginalportions so that the marginal portions lie on the inner surface of therespective webs;

passing the webs and the marginal portions through the ultrasonicwelding unit so as to ultrasonically weld the marginal portions to therespective web and so connect each side of the strip to the webs to formbridging portions in between the webs;

sealing the side portions of the webs;

cutting across and sealing the side sealed webs to form a closed end ofthe gas filter element and separate it from the webs.

In order that the invention may be well understood it will now bedescribed by way of example only with reference to the accompanyingdiagrammatic drawings, in which:

FIG. 1 is a plan view of one filter bag of the invention;

FIG. 2 is a side elevation of the filter bag of FIG. 1;

FIG. 3 is a partial front elevation of the pocket of the filter bag ofFIG. 1 drawn to a much enlarged scale,

FIG. 4 is a much enlarged view of one partition circled in A in FIG. 3;

FIG. 5 shows a flow diagram for one continuous method of manufacture ofa pocket of the filter bag

FIG. 6 is a partial front elevation of another filter bag of theinvention;

FIG. 7 is a view of one partition circle at B in FIG. 6;

FIG. 8 is a perspective view showing part of the mouth of the bag in theopen condition;

FIG. 9 is a section through a frame having pockets showing two pocketpartitions;

FIG. 10 shows a flow diagram for a method of continuous manufacture of apocket of the filter bag of FIGS. 6 to 9; and

FIG. 11 shows in detail the fold up former and an ultrasonic weldingunit used in the method of FIG. 10.

The same reference numerals are used where convenient in describing thedifferent embodiments.

The filter bag shown in FIGS. 1 to 4 comprises two layers L1,L2 of gaspermeable of synthetic fibrous material secured together to provide abag having elongate filter elements, i.e. cells or pockets P which areshown in FIG. 2. The side walls may be formed of any suitable syntheticfibre material or blend of materials. One example is polypropylene. Thematerial may be treated, e.g. with an antimicrobial agent to resistmicrobial mould growth and build up of moulds or mildews. The two layersare sealed together along three sides by double seals S1, as a result ofwhich the pockets are closed at their bottom or distal ends Pb but openat their mouths Pm. As shown in FIG. 1 the bag is generally rectangularas seen in plan. The pockets have a generally rectangular open inlet ormouth Pm, (except for the end ones Pe where they tend to be moretriangular because of the way the two layers L1,L2 are joined together).

According to the invention individual pockets contain partitions 5 toform pocket portions. The partitions 5 are made of webs of fusiblenatural or synthetic sheet material such as polypropylene. The marginalportions 5 a,5 b are sealed to the inside surface of the layers L1,L2respectively. The partitions 5 extend the full distance from the frontto the rear of the bag so that as shown in FIG. 1 there are parallelelongated seams S2. The bag is made in the following general way and asshown in FIG. 5.

The apparatus comprises two rolls of webs W1,W2 which are located one oneach side of two ultrasonic welding units U each made up of a shoe 6 andhorn unit 7 and are fed to extend parallel to each other one on eachside of the units U. Strips or ribbons R of polypropylene are fedbetween the webs to the units U and when the assembly is fed passed theultrasonic welding unit fusion takes place to form he partitions 5.While one unit U is arranged to make a continuous join the other has aninterruption to provide a short length portion of one edge of thepartition to be formed adjacent the intended open inlet so that theformed pocket P can flex at its front end for mounting in a filterheader frame. The sides of the bag precursor are sealed by otherultrasonic welding units U. The formed bag is fed passed a cutting unitC to out an individual bag, the rear end of which is then sealed,preferably heat sealed. This process is continuous, and the parametersmay easily be adjusted according to the nature of the webs, fusiontemperature and time, and dimensions. in a trial, a filter bag of theinvention was tested in the filtration of dust laden air. The bag wasmounted in a frame. It was easy to inflate. There was a high level ofdust collection and a very low overall pressure drop. The filterresistance was controlled. The partitions 5 hold the pockets P incontrolled aerodynamic configuration to ensure a uniform shapeindependent of the rate of air flow. The ultrasonic bonding ensures astrong connection without holes. This eliminates leakage or bypass ofthe particles through such holes. It also avoids the need to sealneedlepunched holes using a hot melt sealant, giving more usefulfiltration area. While we do not intend the invention to be limited bythe following theory, our investigations show that the flow of airthrough the pocket is aerodynamically streamline or laminar, so drawingmore particles therein, and because each pocket is a sealed containervery few if any of the particles escape. Evaluations have show that afilter element according to the invention remains intact anddimensionally stable up to the pressures exceeding 750 pa.

In the embodiment shown in FIGS. 6 to 9, the inlet end of the partition5 is still to form two general parallel side flaps F1,F2 sides separatedby a gap. The slit extends a short distance in from the end, sufficientto give the necessary flexibility according to the strength of thematerials forming the layers L1,L2 and the partition 5. The flaps aresecured to the layers by the double seals 6A,6B which are ultrasonicseals. As a result, the mouth of the pocket can be open in the manner ofjaws, and the engagement of the partition and the walls will not bebroken.

As shown in FIG. 9, the bag is connected to a metal header or frame 10of generally rectangular section. The front portions of adjacent pocketsare crimped or otherwise secured by metal clamps to the edge of theframe. The header or holding frame may be of any suitable type, e.g. forfront, rear or side withdrawal mounting. The frame may be made of metalor plastics.

The bag can be made on a continuous basis in the following way shown inFIGS. 10 and 11.

The apparatus comprises parallel rod-shaped ultrasonic welding units U1,U2 and U3 each made up of a shoe and horn or anvil unit and two rolls ofsynthetic fibrous material W1,W2 which are located on opposite sides ofU1 and U2 and are fed to extend parallel to each other on opposite sidesof U1 and U2 (see FIG. 10). Strips or ribbons R of polypropylene are fedbetween the webs W1, W2 and the units U1 and U2 to fuse both marginaledges R to the web. The sides of the precursor are sealed by otherultrasonic welding units U3. The partly formed bag is fed passed acutting unit C to cut an individual bag, the rear end of which is thensealed, preferably heat sealed. A marginal 5 a,5 b portion of eachpartition 5 near the upstream end of the element is then cut tointroduce the longitudinal slit and form the flaps F1,F2.

As shown in FIG. 11 each strip R is wound off a reel 11 over a roller 12and fed into a former 20 the top edge of which is curved to upturn thetwo margins 5 a,5 b so that the strip is generally channel shaped. Thefolded up strip is then passed through the unit at the lower end ofwhich is an ultrasonic shoe 6 in the form of a wheel having a patternedsurface. The wheel 6 is on a shaft which is rotated by means of a beltdrive 21. Behind the wheel is a web W1,W2 and behind that is the horn 7of the ultrasonic welding unit in line with the wheel. As the margin 5 aof the strip and the web W1 meet the shoe 6 and the horn 7 ultrasonicenergy is applied to fuse them together. (In practice the web comprisesan inner skin and an outer carrier surface with filter media in between;the margin 5 a is fused to the inner skin). Pressure is applied by thearm 31 of a rocker 30 under pneumatic control to urge the margin 5 aonto the web so that there is good contact in between. The welding mustbe sufficient to secure the margin 5 a and the web W1 together but notso strong that either material will be torn in use or be burned by thewelding. The margin 5 b will be welded to the web W2 using another unitfurther down the line.

In a preferred embodiment, not shown, the side seals S1 are made a shortdistance in from the longitudinal edge from the webs and a slitter, notshown, is used to cut away the excess material which is then disposedof.

The invention also includes a method of filtration, comprising passinggas under pressure through a filter element as defined and causing orallowing the particles to collect in the filter pockets. The inventionalso includes apparatus for making the filter elements.

The invention is useful wherever bag filters are suitable. The inventionensures that heavyweights of dust are trapped in the filter elementsover extended maintenance periods; can protect equipment in general airconditioning plant, e.g. in hospitals, communal buildings, officesuites, retail outlets and the like; and reduces energy consumptionbecause of the low initial resistance to air flow.

What is claimed is:
 1. A gas filter element, comprising: first andsecond webs of filter material, each of the webs having opposing leadingand trailing edges which are interconnected by left and right marginalsides, the first and second webs being joined together along theirleading edges and left and right marginal sides to form an open filterbag; a plurality of partition members disposed between said first andsecond webs in spaced apart relationship, the partition membersextending lengthwise through said open filter bag from said leadingedges to said trailing edges to define a series of individual pocketswithin said open filter bag, each of said partition members havingmarginal folded edges extending lengthwise of said partition members,said partition members being sealed to said webs along said marginalfolded edges, each of said partition members including a slit formedtherein that extends a predetermined distance from said trailing edgetoward said leading edges of said webs, said slit defining two sideflaps in each of said partition members, and said partition member sideflaps being double sealed to said webs.
 2. The gas filter element ofclaim 1, wherein said filter material includes a fibrous material. 3.The gas filter element of claim 1, wherein said filter material is apolypropylene fiber.
 4. The gas filter element of claim 1, wherein saidpartitions are formed from strips of fusible material.
 5. The gas filterelement of claim 1, wherein said partitions are sealed to said webs byultrasonic welding.
 6. The gas filter element of claim 1, wherein eachof said partition members has a channel-shaped configuration when viewedfrom an end.
 7. A filter for insertion into a filter header frame, thefilter comprising: a pair of panels formed from a synthetic filtermaterial, each of the panels including opposing first and second endsinterconnected by said edges, said filter panels being joined togetheralong said first and side edges to form a filter bag having fourdistinct edges, the filter bag being sealed along said first and sideedges and open along said second edge so as to define an open mouth ofsaid filter bag along said second edge; a plurality of elongated stripsof fusible material disposed between said panels in spaced-apartrelationship, each of the fusible strips being formed into achannel-shaped strip having folded marginal portions that extendlengthwise of said fusible strips; fusible strips being ultrasonicallysealed to said panels along each of their marginal folded portions so asto define a plurality of individual pockets extending lengthwise of saidfilter bag, each of said fusible strips having longitudinal slips formedtherein which are disposed between said marginal folded portions andwhich extend lengthwise into said fusible strips for a predetermineddistance, the slits defining open jaw portions for each of said strips,the open jaw portions being flanked by a pair of side flaps, the sideflaps being double sealed to said panels to prevent tearing of saidfusible strips at said open jaw portions thereof.
 8. The filter claimedin claim 7, wherein said panels are formed from a polypropylene filter.9. The filter claimed in claim 7, wherein said panels first and sideedges are sealed by ultrasonic welding.
 10. The filter claimed in claim7, wherein said fusible strip side flaps are double sealed by ultrasonicwelding.